Meta-analysis of RNA-Seq studies reveals genes with dominant functions during flower bud endo- to eco-dormancy transition in Prunus species.

In deciduous fruit trees, entrance into dormancy occurs in later summer/fall, concomitantly with the shortening of day length and decrease in temperature. Dormancy can be divided into endodormancy, ecodormancy and paradormancy. In Prunus species flower buds, entrance into the dormant stage occurs when the apical meristem is partially differentiated; during dormancy, flower verticils continue their growth and differentiation. Each species and/or cultivar requires exposure to low winter temperature followed by warm temperatures, quantified as chilling and heat requirements, to remove the physiological blocks that inhibit budburst. A comprehensive meta-analysis of transcriptomic studies on flower buds of sweet cherry, apricot and peach was conducted, by investigating the gene expression profiles during bud endo- to ecodormancy transition in genotypes differing in chilling requirements. Conserved and distinctive expression patterns were observed, allowing the identification of gene specifically associated with endodormancy or ecodormancy. In addition to the MADS-box transcription factor family, hormone-related genes, chromatin modifiers, macro- and micro-gametogenesis related genes and environmental integrators, were identified as novel biomarker candidates for flower bud development during winter in stone fruits. In parallel, flower bud differentiation processes were associated to dormancy progression and termination and to environmental factors triggering dormancy phase-specific gene expression.

The outer influences the inner: Postharvest UV-B irradiation modulates peach flesh metabolome although shielded by the skin.

UV-B-driven modulation of secondary metabolism in peach fruit by enhancing the biosynthesis of specific phenolic subclasses, is attracting interest among consumers. However, current literature explored the UV-B-induced metabolic changes only in peach skin subjected to direct UV-B irradiation. Accordingly, this study aimed to understand whether UV-B radiation penetrates the fruit skin and is able to induce metabolic changes also within the inner flesh. Peaches were UV-B-irradiated either 10 or 60 min, and the flesh was sampled after 24 and 36 h. Non-targeted metabolomics revealed that UV-B has a strong impact on peach flesh metabolome, determining an initial decrease after 24 h, followed by an overall increase after 36 h, particularly for terpenoids, phenylpropanoids, phytoalexins and fatty acids in the 60 min UV-B-treated samples (+150.02, +99.14, +43.79 and +25.44 log2FC, respectively). Transmittance analysis indicated that UV-B radiation does not penetrate below the skin, suggesting a possible signalling pathway between tissues.

Combined transcriptomics and proteomics analysis provides insight into metabolisms of sugars, organic acids and phenols in UV-C treated peaches during storage.

3Ultraviolet-C (UV-C) irradiation is known for prolonging the shelf life of many fruit by regulating different pathways. To better understand the roles of UV-C treatment in regulating the metabolic pathways in peach fruit during cold storage, transcriptomics and proteomics approaches were applied to investigate changes in peaches treated with UV-C (1.5 kJ m-2). The results showed that most differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) were largely matched to carbohydrates and secondary metabolites. Further analysis found that peaches treated with UV-C exhibited higher sucrose, citric acid, malic acid, phenols, flavonoids and anthocyanins compared with untreated peaches. Proteomics and transcriptomics together indicated that changes of sugars and acids were associated with the expressions of invertase, sucrose synthase, fructokinase, malate dehydrogenase and citrate synthase. UV-C irradiation promoted the synthesis of phenols, flavonoids and anthocyanins by up-regulating expressions of phenylalanine ammonia-lyase, 4-coumarate-CoA ligase, chalcone synthase, dihydroflavonol 4-reductase and UDP-glucose:flavonoid glucosyltransferase. In summary, this research explained the general molecular mechanism of the changes of sugars, acids and phenols in peaches in response to UV-C.

Hot air and UV-C treatments promote anthocyanin accumulation in peach fruit through their regulations of sugars and organic acids.

In our present study, we aimed to explore the effects of hot air and UV-C on anthocyanins and the interaction among anthocyanin, sucrose and organic acids in peaches during postharvest storage. Peaches were treated with hot air or UV-C and stored at 1 °C for 35 days. The results showed that both treatments significantly enhanced the accumulation of anthocyanins and suppressed the degradation of sucrose, citric and malic acids. An in vitro test verified that sucrose, citric and malic acid penetrated the tissue and then induced the biosynthesis of anthocyanins by up regulating anthocyanin-related enzymes. In addition, hot air and UV-C directly enhanced the activities and gene expression of related enzymes to promote the accumulation of anthocyanins. PAL, ANS and UFGT played crucial roles in the biosynthesis of anthocyanins in peach fruit after harvest, and these three enzymes can be stimulated by HA, UV-C, sucrose, citric and malic acid.

Postharvest hot air and UV-C treatments enhance aroma-related volatiles by simulating the lipoxygenase pathway in peaches during cold storage.

Hot air (HA) treatment and ultraviolet C (UV-C) irradiation have been demonstrated to control chilling injury in peaches. However, little is known about the effects of HA and UV-C treatments on volatiles changes in peach fruit during cold storage. In this study, peaches were treated with HA at 40 °C for 4 h or irradiated with UV-C lamp (1.5 kJ/m2), and then stored at 1 °C for 35 days plus 3 days of shelf life at 20 °C. Results showed that HA and UV-C suppressed chilling injury significantly, exhibiting lower internal browning index. Also, the two treatments enhanced emissions of esters and lactones in peaches by increasing enzymes of alcohol acyltransferase (AAT), fatty acid desaturase (FAD) acetyl coenzyme A transferase (ACX). These suggested that the increase of fruity note aromas in peaches by the two treatments is closely associated with aroma-related metabolism (LOX pathway and lactone pathway).

Comparative "phenol-omics" and gene expression analyses in peach (Prunus persica) skin in response to different postharvest UV-B treatments.

Ultraviolet-B (UVB) radiation impacts the plant behaviour in many ways, including modifying their secondary metabolism. Although several studies have quantified the UV-B effects on phenolic composition, most of them focused on leaves or investigated a limited amount of phenolics. The present work aimed to investigate the phenolic changes after two postharvest UV-B treatments, 10 and 60 min (1.39 kJ m-2 and 8.33 kJ m-2, respectively), on peach (Prunus persica cv Fairtime) fruit with a non-targeted, whole profiling approach, and targeted gene expression analysis on skin. After both UV-B exposures, peach fruit were harvested at 24 and 36 h for "phenol-omics" analysis, while additional 6 h and 12 h recovery times were used for gene expression analysis. Our results revealed that both UV-B exposures resulted in a decrease of several phenolic compounds, such as anthocyanins, after 24 h from the exposure. In contrast, the expression of the UV-B signalling components, the phenylpropanoid biosynthesis genes and their transcriptional regulators increased 6 h after the treatment, mostly with a UV-B-dose dependent behaviour, preceding an accumulation of most phenolics in both the UV-B treatments at 36 h compared to 24 h. Orthogonal projections to latent structures discriminant analysis (OPLS-DA) revealed that flavonoids, particularly anthocyanins, were the main phenolic subclasses accumulated after UV-B exposure.

Melatonin increases chilling tolerance in postharvest peach fruit by alleviating oxidative damage.

Melatonin has been reported to alleviate chilling symptoms in postharvest peach fruit during cold storage, however, the mechanism involved is largely unknown. To better understand its role in chilling tolerance, here we investigated the effects of melatonin on oxidative damage in peach fruit subjected to chilling after harvest. Chilling injury of peaches was dramatically reduced by melatonin treatment. Melatonin induced hydrogen peroxide (H2O2) content at the early stage of storage but inhibited its accumulation thereafter. Meanwhile, melatonin also up-regulated the expression of genes involved in antioxidant responses in peaches. In addition, compared to the control fruit, peaches treated with melatonin displayed higher transcript abundance of ascorbic acid (AsA) biosynthetic genes and consequently increased the AsA content. Our results suggested that in response to melatonin during chilling, the high H2O2 level in the treated peaches at the initial time of storage, may work as a signaling molecule to induce protective mechanisms via up-regulating the expression of antioxidative genes and increasing AsA content. On the other hand, after the transient increase in the treated peaches, H2O2 was efficiently removed because of the activated antioxidant systems, which was associated with the higher chilling tolerance induced by melatonin.

Analysis of apple beverages treated with high-power ultrasound: a quality function deployment approach.

BACKGROUND: The objective of this paper was to demonstrate application of quality function deployment in analysing effects of high power ultrasound on quality properties of apple juices and nectars. In order to develop a quality function deployment model, joint with instrumental analysis of treated samples, a field survey was performed to identify consumer preferences towards quality characteristics of juices/nectar. RESULTS: Based on field research, the three most important characteristics were 'taste' and 'aroma' with 28.5% of relative absolute weight importance, followed by 'odour' (16.9%). The quality function deployment model showed that the top three 'quality scores' for apple juice were treatments with amplitude 90 µm, 9 min treatment time and sample temperature 40 °C; 60 µm, 9 min, 60 °C; and 90 µm, 6 min, 40 °C. For nectars, the top three were treatments 120 µm, 9 min, 20 °C; 60 µm, 9 min, 60 °C; and A2.16 60 µm, 9 min, 20 °C. CONCLUSION: This type of quality model enables a more complex measure of large scale of different quality parameters. Its simplicity should be understood as its practical advantage and, as such, this tool can be a part of design quality when using novel preservation technologies. © 2017 Society of Chemical Industry.

Identification and characterization of Prunus persica miRNAs in response to UVB radiation in greenhouse through high-throughput sequencing.

BACKGROUND: MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression of target mRNAs involved in plant growth, development, and abiotic stress. As one of the most important model plants, peach (Prunus persica) has high agricultural significance and nutritional values. It is well adapted to be cultivated in greenhouse in which some auxiliary conditions like temperature, humidity, and UVB etc. are needed to ensure the fruit quality. However, little is known about the genomic information of P. persica under UVB supplement. Transcriptome and expression profiling data for this species are therefore important resources to better understand the biological mechanism of seed development, formation and plant adaptation to environmental change. Using a high-throughput miRNA sequencing, followed by qRT-PCR tests and physiological properties determination, we identified the responsive-miRNAs under low-dose UVB treatment and described the expression pattern and putative function of related miRNAs and target genes in chlorophyll and carbohydrate metabolism. RESULTS: A total of 164 known peach miRNAs belonging to 59 miRNA families and 109 putative novel miRNAs were identified. Some of these miRNAs were highly conserved in at least four other plant species. In total, 1794 and 1983 target genes for known and novel miRNAs were predicted, respectively. The differential expression profiles of miRNAs between the control and UVB-supplement group showed that UVB-responsive miRNAs were mainly involved in carbohydrate metabolism and signal transduction. UVB supplement stimulated peach to synthesize more chlorophyll and sugars, which was verified by qRT-PCR tests of related target genes and metabolites' content measurement. CONCLUSION: The high-throughput sequencing data provided the most comprehensive miRNAs resource available for peach study. Our results identified a series of differentially expressed miRNAs/target genes that were predicted to be low-dose UVB-responsive. The correlation between transcriptional profiles and metabolites contents in UVB supplement groups gave novel clues for the regulatory mechanism of miRNAs in Prunus. Low-dose UVB supplement could increase the chlorophyll and sugar (sorbitol) contents via miRNA-target genes and therefore improve the fruit quality in protected cultivation of peaches.

UV-B irradiation differentially regulates terpene synthases and terpene content of peach.

Plants generate protective molecules in response to ultraviolet (UV) light. In laboratory experiments, 48 h UV-B irradiation of peach fruits and leaves reduced the flavour-related monoterpene linalool by 60%. No isoprene was detected, but other terpenoids increased significantly, including a threefold accumulation of the sesquiterpene (E,E)-α-farnesene, which was also increased by jasmonic acid treatment. RNA sequencing revealed altered transcript levels for two terpene synthases (TPSs): PpTPS1, a TPS-g subfamily member, decreased by 86% and PpTPS2, a TPS-b subfamily member, increased 80-fold. Heterologous expression in Escherichia coli and transient overexpression in tobacco and peach fruits showed PpTPS1 was localized in plastids and associated with production of linalool, while PpTPS2 was responsible for (E,E)-α-farnesene biosynthesis in the cytoplasm. Candidate regulatory genes for these responses were identified. Commercial peach production in Asia involves fruit bagging to maintain marketable yield and quality. TPS gene expression and volatile terpenoid production in field experiments, using bags transmitting high UV-B radiation, showed similar effects on peach volatiles to those from laboratory experiments. Bags transmitting less UV-B light ameliorated the reduction in the flavour volatile linalool, indicating that flavour components of peach fruits can be modulated by selecting an appropriate source of environmental screening material.

Inhibitory effect of microwaved thinned nectarine extracts on polyphenol oxidase activity.

By-products from agricultural practices or from the fruit processing industry are a source of bioactive compounds that could be used in the food industry. Such by-products include thinned fruits, which are expected to contain high quantities of interesting compounds. One possible application of this fruits is the prevention of the enzymatic browning suffered by fruits and vegetables after minimal processing. The aim of this study is to determine the in vitro and in vivo activity of microwaved extracts obtained from thinned nectarines. It has been observed that in vitro the extracts obtained after the application of high microwave power levels (500, 1000 and 1500 W) are mixed type inhibitors of polyphenoloxidase enzyme, showing an irreversible inactivation. This inhibition could be attributed to the Maillard reaction products formed during the microwave treatment. In vivo, a solution of 2% of the extract obtained at 1500 W inhibited the enzymatic browning in minimally processed peaches for 8 days of storage.

Potential of carboxymethyl cellulose and γ-irradiation to maintain quality and control disease of peach fruit.

Carboxymethyl cellulose (CMC) coatings alone and in combination with gamma irradiation were tested for maintaining the storage quality and control of post-harvest gray and black mold disease of peach. Matured green peaches were CMC coated at levels 0.5-1.0% (w/v) and gamma irradiated at 1.2 kGy. The treated fruit including control was stored under ambient (temperature 25 ± 2°C, RH 70%) and refrigerated (temperature 3 ± 1°C, RH 80%) conditions. In fruits treated with individual treatments of 1.0% (w/v) CMC; 1.2 kGy irradiation and combination of 1.0% (w/v) CMC and 1.2 kGy irradiation, no decay was recorded up to 6, 8 and 14 days of ambient storage. Irradiation alone at 1.2 kGy prevented the onset of disease incidence up to 4 days compared to 2 days by 1.0% (w/v) CMC coating following 30 days of refrigeration. Combination of CMC at 1.0% (w/v) and 1.2 kGy irradiation prevented disease incidence of peach up to 7 days during post-refrigerated storage at 25 ± 2°C, RH 70% following 30 days of refrigeration. Above combinatory treatment can be of great potential in facilitating the marketing of the fruit, thereby benefiting the growers.

Cell wall metabolism of peaches and nectarines treated with UV-B radiation: a biochemical and molecular approach.

BACKGROUND: Ultra-violet B (UV-B) radiation has been shown to improve, at least in selected genotypes, both the health-promoting potential and the aesthetic properties of tomato and peach fruits during their post-harvest period. The effects of post-harvest UV-B treatment on the cell-wall metabolism of peaches and nectarines (Prunus persica L. Batsch) were assessed in this study. Three cultivars, Suncrest (melting flesh, MF) and Babygold 7 (non-melting flesh, NMF) peaches and Big Top (slow melting, SM) nectarine, differing in the characteristics of textural changes and softening during ripening, were analysed. RESULTS: The effects of UV-B differ in relation to the cultivar considered. In MF 'Suncrest' fruit, UV-B treatment significantly reduced the loss of flesh firmness despite the slight increase in the presence and activity of endo-polygalacturonase. The activity of exo-polygalacturonase increased as well, while endo-1,4-ß-D-glucanase/ß-D-glucosidase, ß-galactosidase and pectin methylesterase were substantially unaffected by the treatment. The UV-B-induced reduction of flesh softening was paralleled by the inhibition of PpExp gene transcription and expansin protein accumulation. The UV-B treatment did not induce differences in flesh firmness between control and UV-B-treated NMF 'Babygold 7' and SM 'Big Top' fruit. CONCLUSION: Based on these results, post-harvest UV-B treatment may be considered a promising tool to improve shelf-life and quality of peach fruit.

Ultraviolet-B radiation applied to detached peach fruit: A study of free radical generation by EPR spin trapping.

In peaches, phenolic compounds are the major sources of antioxidants, and cyanidin-3-O-glucoside is the main anthocyanin present, above all in the skin. Anthocyanin content has been shown to increase after UV-B irradiation, which may be very harmful for all biological organisms due to the induction of the generation of reactive oxygen species (ROS). Peach fruits (cv. 'Suncrest') were exposed during post-harvest to supplemental ultraviolet-B radiation. A spin-trapping technique was used to monitor the generation of free radicals under UV-B, and 5-(diethoxy-phosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) was used as the spin trap. The flesh of peaches was essentially unaffected by the treatment, whereas the skin was responsive at the end of the treatment, accumulating ascorbate, flavonoids, cyanidin-3-O-glucoside, and showing a higher antioxidant activity. The levels of stable free radicals were also lower at the end of treatment. Carbon-centred radicals contributed the most to the total amounts of free radicals, whereas hydroxyl radicals and oxygen-centred free radicals contributed minimally. The carbon-centred free radical identified was the same as the one obtained after irradiation of authentic cyanidin-3-O-glucoside. During UV-B treatment cyanidin-3-O-glucoside increased and was capable of radicalization protecting the other organic molecules of the cell from oxidation. ROS, among which hydroxyl radicals, were thus maintained to minimal levels. This ability of cyanidin-3-O-glucoside displayed the mechanism underlined the tolerance to UV-B irradiation indicating that shelf life can be prolonged by the presence of anthocyanins. Thus, UV-B technique results a good approach to induce antioxidant production in peach fruits increasing their nutraceutical properties.